1. Field of the Invention
The present invention relates to a video camera apparatus that permits exchanges of control signals and camera output signals between a video camera and a camera control unit over a radio channel.
2. Description of the Prior Art
Video cameras for use by broadcasting stations are each controlled by a separately provided camera control unit (called a CCU) in diaphragm opening and other settings. The camera is also controlled by the CCU so that the signal output by the camera will be synchronized with an externally furnished reference video signal (i.e., placed under genlock control).
During a camera-based program broadcast, each participating video camera is generally connected to its camera control unit via cables such as triax. In some cases, cable-based connections are unavailable between the video camera and the CCU; these physical connections are then replaced by radio communications.
The radio communications from each video camera to the CCU involve the use of a microwave circuit. On the other hand, control commands from the CCU to each video camera are transmitted over a radio channel for voice communication.
Conventional camera control systems in which video cameras are each connected to a CCU by radio communication have some disadvantages that are not experienced with the cable-based camera-to-CCU connection. Some of these disadvantages will be discussed below.
Where a video camera and a CCU are connected by cable, CCU-initiated control commands and camera-initiated commands are transmitted bidirectionally therebetween. That is, the CCU transmits control commands to the camera over the cable. In turn, the video camera sends to the CCU over the same cable such commands as a camera status signal (defining camera diaphragm setting, etc.) and a call command by which the camera operator calls up the CCU.
Where the video camera and the CCU are connected by radio channel, the commands are transmitted unidirectionally, i.e., only from the CCU to the camera as described. It is impossible for the camera to send the camera status signal, call command or other commands to the CCU over the radio channel.
The radio channel for control command transmission is a voice communication radio channel. This means that when a genlock reference signal is sent to the camera over the radio channel, genlock control becomes very vulnerable to external disturbances. With the genlock control signal sent over the conventional voice communication radio channel, the genlock system is markedly susceptible to Doppler shifts. Furthermore, the lock range is narrow and phase jitter plentiful with the genlock system. Thus the genlock of the output video signal is much less stable with the radio-based connection between camera and CCU than with the cable-based connection therebetween.